1. Field of the Invention
The present invention relates to a small thin film movable element and a small thin film movable element array as well as a method of driving a small thin film movable element for displacing a movable portion by an electrostatic force in accordance with a voltage applied to a movable electrode and a fixed electrode.
2. Description of the Related Art
In recent tears, by rapid progress of an MEMS technology (MEMS; Micro-Electro Mechanical Systems), there has been intensively carried out a development of a small thin film movable element for electrically displacing/moving a small thin film of μm order (refer to, for example, JP-T-10-510374 and JP-A-8-334709). As the small thin film movable element, there are, for example, a digital micromirror device (DMD) for deflecting light by inclining a micromirror, an optical switch for switching an optical path, an RF switch for connecting and switching an RF (high frequency) signal and the like. In a field of an optical information processing, DMD is provided with a wide use of a projecting display, a video monitor, a graphic monitor, a television set and electrophotography printing and the like. Further, application of an optical switch is expected in optical communication, optical interconnection (a signal connection technology by light such as an intercoupling network by parallel computers), an optical information processing (information processing by optical operation) and the like.
A small thin film movable element generally includes a movable portion which is supported elastically displaceably and is displaced bi-directionally, and the movable portion mainly deals with switching operation. Therefore, a control of braking a movable portion becomes particularly important in carrying out excellent switching operation.
In the related art, in a control of braking a movable portion of a small thin film movable element of this kind, it is general to start to displace a movable portion to a desired fixed electrode from a stationary state of the movable portion (a state in which the movable portion is not vibrated). That is, for example, according to a small thin film movable element in which a movable portion is pivoted centering on a hinge, when a drive voltage is applied to a movable electrode provided at the movable portion and a fixed electrode provided at a board, an electrostatic force is operated to the movable portion and the fixed electrode, and the movable portion is attracted to the board against a gravitational force, an elastic force of the hinge. A state in which the movable portion is pivoted to displace by the electrostatic force and a pivoting front end is adsorbed (pulled) to the board is referred to as (Pull-in).
In a case of a small thin film movable element, generally, when a drive voltage is made ON from an OFF state, as shown by FIG. 19A, there is brought about a transition period of a movable portion until the movable portion is completely pulled in. That is, a delay is produced until the movable portion is operated to be ON substantially from ON of the drive voltage. The delay is produced similarly even in a case of making the drive voltage OFF from an ON state as shown by FIG. 19B.
Under such a situation, when a small thin film movable element is used in, for example, an exposing apparatus, according to the exposing apparatus, the movable portion is operated to be ON substantially when the drive voltage to the small thin film movable element is made ON and thereafter operated and therefore, by a difference in timings when the movable portion is made OFF from ON and made ON from OFF, a difference in an optical amount is brought about to pose a problem that an amount of exposing a photosensitive member is varied.